Asphalt roadway.



E. M. UHADBOURNE.

A$PHALT ROADWAY.

APPLICATION FILED MAYZS], 1911 1,098,? 1 O. Patented June 2, 19 14.

avwawtoz snwssn M. omnnousun, or SAN rnauoxsco. car-rec des ASEEALT ROADWAY.

To all who-m it may concern Be it lmown that I, EDWARD M. CHM BOURKE, a citizen of the United States, residing at San Francisco, in-the county of San Francisco and State of Galiforhimhave invented a certain new and useful Improve- .ment in Asphalt Roadways; and I do hereby declare the following to be a full, clear, and exact description of the same, reference being had to the accompanying drawings,

forming a part of this specification, and to the figures and letters of reference marked thereon. v

This invention relates to the construction of pavement for roadways and more especially to that type wherein the surface is formcd'by a rock or stone aggregate combined with an asphaltic binder Which is sub s'tantially non-fluid at ordinary temperatures, but capable of being renderedglimpid or liquid by heat. The surface layer is usually supported by a suitable foundation, such as cement concrete; macadam; approved practice indicating the desirability of forming the surface of the base with pockets or irregularities as set forth, for instance,

in no prior Patents Nos. 956,940,, 965,562l

and 9823i? and the present inventionwil be described under theuassumption, that a foundation of the'cha'racter stated; is em ployed. In so far as the pavement produced is concerned, itis the object of the invention to form a surface layer Which will be a homogeneous mass, substantially free from voids and with such proportions of aggregate and binder as will afford a maximum resistance 'to Wear and displacement under traflic conditions and at the same time conform to approved practice'vvith res ect to surface conditions and resiliency or absorbing shock and vibration Without disintegration.

. In so far the process of producing the pavement isconcerned, the ob ects of the nvention are, to reduce the number of steps and machinery necessary for handling and combining the'ingredients; to bring the'ini 'gredients together in such manner that the voids in the aggregate are filled by capillary action and downward penetration from above, and to permit of the use of a cheap and easily prepared or obtained aggregate. Attempts 'havdheretofore been made to Specification of Letters Patent.

Patented June 2, 1911.4.

application filed May 29, 1911. Serial No. 630,068.

produces. homogeneous layer of a e ate. and aspnaltic binder-for roadway g fa oesx For instance, it has been proposed to grade" the aggregate and to combine the graded" material in certain proportions and sizes, and to mix the binder therewithby agita tion and heat, the completely mixed aggro gate and binder being carried to and deposited on-th roadway Whereit is spread and rolled, butsuch operations do not result in as homogeneous mixture, as the particles stick together vvhen suddenly cooling, formingmasses, some or all of which have larger proportions of certain sizes of the aggregate than others, and the binder is caused to drain out because of its hot liquid state, and only coat the particles and not fill the voids.

When laid and rolled not only is it impossi- I ble to prevent the leaving of a percentageof voids, but owing to the irregularity of the mixture, the surface layer willyvear and disintegrate. irregularly. It has also been proposed to pour a hot asphalt binder over a layer of coldaggregate With a, large per.-

centage of voids amounting to about 50% of thetotal' volume, but owing tothe rapid cooling of the binder, when it comes in con-v tact with the cold aggregate, irregular penetration results; furthermore, the adhesion between the aggregate and the asphalt. binder is not stronger lasting. A great quantity of asphalt binder is used endeavoring to fill the ,voids in the aggregate with the result that the asphalt binderbecomes a 'Wear resistant material, a use for which it was never intended.

In accordance with the present invention the foundation is prepared preferably-of cement concretefand suitable provision at the top surface'such as pockets or irregularities' tobond the surface to the base more securely." Upon" this foundation there is spread-evenly player of which the binder is 'to be combined. The

hot aggregate with aggregate is composed of broken'natural stone mixed- With sand or sand alone, the larger pieces-of which er: of less diametcr thanthe thickness of the layer of which thev' forms part. The aggregate of sand shoiild be such that it has "from 25% to 40% voids"as.-it" =i's vvlthinthese limitsthat effectthe capillary ""a btionand absorption will draw the binder downand causethe same to spread uniformly through the mass orlayer of a gate. Should the percentage of voids be larger, the interstices are too large hold the hot liquid asphalt binder in sus- "nsion by surface'tension or for capillarto act cil'cetively with the result thatthc .lnllililih hinder would flow away and be of no use, it simply coating some particles of g'rcgate and leaving the rest bare. Should the percentage of voids be smaller, capil lary action and downward ercolation are lpllocked, probably because t e finer particles float in the binder and close the passageways or render the binder too viscid to feed by capillarity. The aggregate preferably iployed consists of 50% broken stone SllCl will pass 31" vor 1 mesh mixeddry with 50% of sand, having between and o?? of voids, or a torpedo sand alone with roximatelythe same quantity of voids. l. is aggregate is heated to a high ternporature and distributed in an even layer over the base and'while in this hot condition a binder containing a large ercentage of asphalt, said binder being su stantially .nmrfiuid in ordinary temperature, but cado of bcin rendered liquid or fluid by heat is pourc over the surface of the same. he layer of aggregate preferably a prox mt ill thickness the thickness of t e sun c lever desired and the thickness of the binder is such that approximately o of it will be absorbed by the l regate. in other words, the l i als the void volume of the aggro-- The practical result" of the action of c the binder'on the hot aggregate lcr the former limpi'd and in condi- This n In' place almost lmmc lately and lung-h there is a large volume of binder l absorbed in proportion to the volume tion into the aggre ate.

each oi: the liner particles of the aggreiilcation, it is believed are fairly well defined by the percentage of voids in the aggregate and to he, as belorc sta 11, between 25"and 40%.

-usduul rock or gravel and the additionof ordinary sand 18 suliicicnt to either reduce mepercentagc of voids when too great or increase the percentage of voids when too anudi. 1

like accompanying drawing shows a secl by capillary action and down- 0,,1hestored heat due to the presence of,

grade and the w size as to absorb and retain by surface ten- To bring the percentage f voids withinthese limits, a comparatively rough; grading is all. that is necessary with any tion of the roadway and illustrates th process of layin the same.

In said diawing A is the cement concrete base; l3 is a hot layer of aggregate having approximately 01'' large Plll'tb ole-s d and 50% 01': small particles (2, the latter having bctwccu and 4-07, of voids.

(.l is a layer of normally non-fluid as phaltic binder poured on the hot aggregate.

E is a finished section in which the binder, has fed down by capillary attrac tion, and percolation into the layer of a grcgutc so as to completely fill the vol s therein.

After the binder has been. melted and absorbed and the-layer is partly cooled, the surface is preferably smoothed and evened by rolling with a smooth roller.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. The method of pavement construction which consists in providing an aggregate composed of a mixture of wear resistant stone and sand, the interstices in the sand being of such size as to exert capillary at traction and absorption, on an asphaltic binder capable of being liquefied by heat, then heating and Sjfl ltfiiltllllg the mixture of stone and sand on a suitable foundation in a layer with its surface conforming to the desired grade and finally filling the interstices therein from the top by capillary action and percolation with u nornnilly nonflliid asphaltic binder rendered limpid by heat, whereby a, homogeneous layer is pro duccd having no excess of either hinder or aggregate.

E2. The method of pavcn'lcntconstruction which. consists in spreading on a supporting foundation a layer oi heated aggregate hav' ing from25% to 40% of voids, and in applying thereto an asphalt binder capable of being rendered limpid by heat whereby the stored heat in the aggregate retains the binder in a liquid state until it can be ab sorbed by downward percolation and capil lary attraction into the aggregate.

3. The method of PdYCHiGIlb construction which consists in providing a layer of heated aggregate composed oi: a mixture of iwcai rcsistant stone and sand with its surface substantially conforming to the desired o'l. which are of such sion at liquid bituminous compound, and in distributing over said-aggregate a substantially uniiorm layer of bituminous com- ,pound non-fluid at ordinary temperatures, but capable of being liquefied by heat,

whereby the bituminous compound is absorbed and held in the voids of the aggregate until cool and non-fluid.

4. The method or pavement construction which consists first in preparing a, suitable 111g not less than 25% or more than 40% foundation; secondly, spreading on said I b the voids in the aggregate are filled from foundation :1 layer of heated aggregate hava ove by penetration.

of voids; and thirdly, pouring over said ARD CHADBOIJI\\E layer of heated aggregate a binder capable Witnesses: of being rendered iimpid by heatbut which M. T. LIARRIAM,,JI., at ordinary temperatures is non-fluid WhBP- Tues. J. STRAUB. 

